lncfg: add postgres

sample-lnd.conf

@@ -1135,6 +1135,13 @@ litecoin.node=ltcd
 ; testing with embedded etcd.
 ; db.etcd.embedded_log_file=/path/etcd.log
 
+[postgres]
+; Postgres connection string.
+; db.postgres.dsn=postgres://lnd:lnd@localhost:45432/lnd?sslmode=disable
+
+; Postgres connection timeout. Valid time units are {s, m, h}. Set to zero to
+; disable.
+; db.postgres.timeout=
 
 [cluster]